If you know spin and you read those answers carefully, you can see that what you hear in the movie may be pro singers dubbed over. I'm not saying I know for a fact, just that the language in those quotes is not exactly definitive.
– user38404Jul 28 '16 at 8:50

Adam DeVine [who plays TheTreblemakers' lead singer] is a great
singer. Lots of confidence. In fact, he's probably as good as a lot of
other singers we work with. He was really prepared, he knew all his
lines, he knew the song really well and he knew what he could do with
his voice.

It's worth noting that some of the cast (Anna Kendrick for example) grew up doing musical theatre so she's been singing for years. It's just that we're only used to seeing her act on screen - her Autobiography isn't bad for a bit of background on what she did before she was famous
– LiathJul 3 at 12:14

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